The Experts below are selected from a list of 234021 Experts worldwide ranked by ideXlab platform
Brian D. O. Anderson - One of the best experts on this subject based on the ideXlab platform.
-
Critical Density for connectivity in 2d and 3d wireless multi hop networks
IEEE Transactions on Wireless Communications, 2013Co-Authors: Seh Chun Ng, Brian D. O. AndersonAbstract:In this paper we investigate the Critical node Density required to ensure that an arbitrary node in a large-scale wireless multi-hop network is connected (via multi-hop path) to infinitely many other nodes with a positive probability. Specifically we consider a wireless multi-hop network where nodes are distributed in \mathbb{R}^d (d = 2,3) following a homogeneous Poisson point process. The establishment of a direct connection between any two nodes is independent of connections between other pairs of nodes and its probability satisfies some intuitively reasonable conditions, viz. rotational and translational invariance, non-increasing monotonicity, and integral boundedness. Under the above random connection model we first obtain analytically the upper and lower bounds for the Critical Density. Then we compare the new bounds with other existing bounds in the literature under the unit disk model and the log-normal model which are special cases of the random connection model. The comparison shows that our bounds are either close to or tighter than the known ones. To the best of our knowledge, this is the first result for the random connection model in both 2D and 3D networks. The result is of practical use for designing large-scale wireless multi-hop networks such as wireless sensor networks.
-
GLOBECOM - Analytical Bounds on the Critical Density for Percolation in Wireless Multi-Hop Networks
2011 IEEE Global Telecommunications Conference - GLOBECOM 2011, 2011Co-Authors: Guoqiang Mao, Brian D. O. AndersonAbstract:In this paper we develop analytical bounds on the Critical Density for percolation in wireless multi- hop networks, but in contrast to other studies, under a random connection model and with nodes Poissonly distributed in the plane $\mathbb{R}^2$. The establishment of a direct connection between any two nodes follows a random connection model satisfying some intuitively reasonable conditions, i.e. rotational and translational invariance, non- increasing monotonicity and integral boundedness. It is well known that under the above network model and connection model there exists a Critical Density below which almost surely a fixed but arbitrary node is connected (via single or multi-hop path) to finite number of other nodes only, and above which the node is connected to an infinite number of other nodes with a positive probability. In this paper we investigate the bounds on the Critical Density. The result is compared with the existing results under a specific connection model, i.e. the unit disk communication model, and it is shown that our method generates bounds close to the known ones. The result provides valuable insight into the design of large- scale wireless multi-hop networks.
S Adlakha - One of the best experts on this subject based on the ideXlab platform.
-
Critical Density thresholds for coverage in wireless sensor networks
Wireless Communications and Networking Conference, 2003Co-Authors: S Adlakha, M SrivastavaAbstract:Sensor networks are deployed to monitor the physical world and to provide relevant data to the users. An important question in such networks is to estimate the number of sensors required to achieve complete coverage of the desired region. The number of sensors required would depend upon the physical characteristics of the individual sensors as well as the nature of the target. In this paper, we address the problem of finding the Critical Density of sensors for complete coverage. We use an exposure-based model to find the number of sensors required to cover an area for given sensor and target characteristics. The accuracy of the results is established via simulations.
-
WCNC - Critical Density thresholds for coverage in wireless sensor networks
2003 IEEE Wireless Communications and Networking 2003. WCNC 2003., 1Co-Authors: S Adlakha, M.b. SrivastavaAbstract:Sensor networks are deployed to monitor the physical world and to provide relevant data to the users. An important question in such networks is to estimate the number of sensors required to achieve complete coverage of the desired region. The number of sensors required would depend upon the physical characteristics of the individual sensors as well as the nature of the target. In this paper, we address the problem of finding the Critical Density of sensors for complete coverage. We use an exposure-based model to find the number of sensors required to cover an area for given sensor and target characteristics. The accuracy of the results is established via simulations.
Zheng-ming Sheng - One of the best experts on this subject based on the ideXlab platform.
-
dense gev electron positron pairs generated by lasers in near Critical Density plasmas
Nature Communications, 2016Co-Authors: Xinglong Zhu, Zheng-ming Sheng, Yan Yin, Ion Cristian Edmond Turcu, A PukhovAbstract:Pair production can be triggered by high-intensity lasers via the Breit-Wheeler process. However, the straightforward laser-laser colliding for copious numbers of pair creation requires light intensities several orders of magnitude higher than possible with the ongoing laser facilities. Despite the numerous proposed approaches, creating high-energy-Density pair plasmas in laboratories is still challenging. Here we present an all-optical scheme for overdense pair production by two counter-propagating lasers irradiating near-Critical-Density plasmas at only ∼1022 W cm-2. In this scheme, bright γ-rays are generated by radiation-trapped electrons oscillating in the laser fields. The dense γ-photons then collide with the focused counter-propagating lasers to initiate the multi-photon Breit-Wheeler process. Particle-in-cell simulations indicate that one may generate a high-yield (1.05 × 1011) overdense (4 × 1022 cm-3) GeV positron beam using 10 PW scale lasers. Such a bright pair source has many practical applications and could be basis for future compact high-luminosity electron-positron colliders.
-
collisionless electrostatic shock formation and ion acceleration in intense laser interactions with near Critical Density plasmas
Physics of Plasmas, 2016Co-Authors: M Liu, Zheng-ming Sheng, Suming Weng, D W Yuan, Min Chen, P Mulser, M Murakami, X L Zheng, Jie ZhangAbstract:Laser-driven collisionless electrostatic shock formation and the subsequent ion acceleration have been studied in near Critical Density plasmas. Particle-in-cell simulations show that both the speed of laser-driven collisionless electrostatic shock and the energies of shock-accelerated ions can be greatly enhanced due to fast laser propagation in near Critical Density plasmas. However, a response time longer than tens of laser wave cycles is required before the shock formation in a near Critical Density plasma, in contrast to the quick shock formation in a highly overdense target. More important, we find that some ions can be reflected by the collisionless shock even if the electrostatic potential jump across the shock is smaller than the ion kinetic energy in the shock frame, which seems against the conventional ion-reflection condition. These anomalous ion reflections are attributed to the strong time-oscillating electric field accompanying the laser-driven collisionless shock in a near Critical Density...
-
collisionless electrostatic shock formation and ion acceleration in intense laser interactions with near Critical Density plasmas
arXiv: Plasma Physics, 2016Co-Authors: M Liu, Zheng-ming Sheng, Suming Weng, D W Yuan, Min Chen, P Mulser, M Murakami, X L Zheng, Jie ZhangAbstract:Laser-driven collisonless electrostatic shock formation and the subsequent ion acceleration have been studied in near Critical Density plasmas. Particle-in-cell simulations show that both the speed of laser-driven collisionless electrostatic shock and the energies of shock-accelerated ions can be greatly enhanced due to fast laser propagation in near Critical Density plasmas. However, a response time longer than tens of laser wave cycles is required before the shock formation in a near Critical Density plasma, in contrast to the quick shock formation in a highly overdense target. More important, we find that some ions can be reflected by the collisionless shock even if the electrostatic potential jump across the shock is smaller than the ion kinetic energy in the shock frame, which seems against the conventional ion-reflection condition. These anomalous ion reflections are attributed to the strongly time-oscillating electric field accompanying laser-driven collisionless shock in a near Critical Density plasma.
-
Relativistic Critical Density increase and relaxation and high-power pulse propagation
Physics of Plasmas, 2012Co-Authors: Suming Weng, Peter Mulser, Zheng-ming ShengAbstract:High‐power laser pulse propagation in an overdense plasma due to the relativistic Critical Density increase has been investigated in one dimension. In a first step the conditions for the existence of a relativistic Critical Density are delimited and supported by particle‐in‐cell simulations. Its accurate determination is made possible by the installation of a new numerical diagnostics. Guided by this we show that the Critical Density increase strongly depends on both laser polarization and plasma Density profile. Further, we find a new relaxation time ranging from several to many laser cycles, which sets a limit for short laser pulse manipulation and tailoring. Paramountly, it is proved that in the power optics domain the pulse propagation velocity is inhibited by the relativistic energy Density in the medium and by the efficient reflection, in contrast to the group velocity from standard dispersion optics.
-
Anisotropic filamentation instability of intense laser beams in plasmas near the Critical Density.
Physical Review E, 2001Co-Authors: Zheng-ming Sheng, Katsunobu Nishihara, Tetsuya Honda, Yasuhiko Sentoku, Kunioki Mima, Sv BulanovAbstract:The relativistic filamentation instability (RFI) of linearly polarized intense laser beams in plasmas near the Critical Density is investigated. It is found that the RFI is anisotropic to transverse perturbations in this case; a homogeneous laser beam evolves to a stratified structure parallel to the laser polarization direction, as demonstrated recently with three-dimensional particle-in-cell simulations by Nishihara et al. [Proc. SPIE 3886, 90 (2000)]. A weakly relativistic theory is developed for plasmas near the Critical Density. It shows that the anisotropy of the RFI results from a suppression of the instability in the laser polarization direction due to the electrostatic response. The anisotropic RFI is also analyzed based on an envelope equation for the laser beam. Finally, the envelope equation is solved numerically, and anisotropic filamentation and self-focusing are illustrated.
Jie Zhang - One of the best experts on this subject based on the ideXlab platform.
-
collisionless electrostatic shock formation and ion acceleration in intense laser interactions with near Critical Density plasmas
Physics of Plasmas, 2016Co-Authors: M Liu, Zheng-ming Sheng, Suming Weng, D W Yuan, Min Chen, P Mulser, M Murakami, X L Zheng, Jie ZhangAbstract:Laser-driven collisionless electrostatic shock formation and the subsequent ion acceleration have been studied in near Critical Density plasmas. Particle-in-cell simulations show that both the speed of laser-driven collisionless electrostatic shock and the energies of shock-accelerated ions can be greatly enhanced due to fast laser propagation in near Critical Density plasmas. However, a response time longer than tens of laser wave cycles is required before the shock formation in a near Critical Density plasma, in contrast to the quick shock formation in a highly overdense target. More important, we find that some ions can be reflected by the collisionless shock even if the electrostatic potential jump across the shock is smaller than the ion kinetic energy in the shock frame, which seems against the conventional ion-reflection condition. These anomalous ion reflections are attributed to the strong time-oscillating electric field accompanying the laser-driven collisionless shock in a near Critical Density...
-
collisionless electrostatic shock formation and ion acceleration in intense laser interactions with near Critical Density plasmas
arXiv: Plasma Physics, 2016Co-Authors: M Liu, Zheng-ming Sheng, Suming Weng, D W Yuan, Min Chen, P Mulser, M Murakami, X L Zheng, Jie ZhangAbstract:Laser-driven collisonless electrostatic shock formation and the subsequent ion acceleration have been studied in near Critical Density plasmas. Particle-in-cell simulations show that both the speed of laser-driven collisionless electrostatic shock and the energies of shock-accelerated ions can be greatly enhanced due to fast laser propagation in near Critical Density plasmas. However, a response time longer than tens of laser wave cycles is required before the shock formation in a near Critical Density plasma, in contrast to the quick shock formation in a highly overdense target. More important, we find that some ions can be reflected by the collisionless shock even if the electrostatic potential jump across the shock is smaller than the ion kinetic energy in the shock frame, which seems against the conventional ion-reflection condition. These anomalous ion reflections are attributed to the strongly time-oscillating electric field accompanying laser-driven collisionless shock in a near Critical Density plasma.
-
highly collimated monoenergetic target surface electron acceleration in near Critical Density plasmas
Applied Physics Letters, 2015Co-Authors: J Y Mao, Liming Chen, Kai Huang, J R Zhao, Wenchao Yan, J L, Martin Aeschlimann, Z Y Wei, Jie ZhangAbstract:Optimized-quality monoenergetic target surface electron beams at MeV level with low normalized emittance (0.03π mm mrad) and high charge (30 pC) per shot have been obtained from 3 TW laser-solid interactions at a grazing incidence. The 2-Dimension particle-in-cell simulations suggest that electrons are wake-field accelerated in a large-scale, near-Critical-Density preplasma. It reveals that a bubble-like structure as an accelerating cavity appears in the near-Critical-Density plasma region and travels along the target surface. A bunch of electrons are pinched transversely and accelerated longitudinally by the wake field in the bubble. The outstanding normalized emittance and monochromaticity of such highly collimated surface electron beams could make it an ideal beam for fast ignition or may serve as an injector in traditional accelerators.
Carlos Cabrelli - One of the best experts on this subject based on the ideXlab platform.
-
multi tiling sets riesz bases and sampling near the Critical Density in lca groups
Advances in Mathematics, 2015Co-Authors: Elona Agora, Jorge Antezana, Carlos CabrelliAbstract:Abstract We prove the existence of sampling sets and interpolation sets near the Critical Density, in Paley Wiener spaces of a locally compact abelian (LCA) group G. This solves a problem left by Grochenig, Kutyniok, and Seip (2008) [7] . To achieve this result, we prove the existence of universal Riesz bases of characters for L 2 ( Ω ) , provided that the relatively compact subset Ω of the dual group G ˆ satisfies a multi-tiling condition. This last result generalizes Fuglede's theorem, and extends to LCA groups setting recent constructions of Riesz bases of exponentials in bounded sets of R d .
-
multi tiling sets riesz bases and sampling near the Critical Density in lca groups
arXiv: Classical Analysis and ODEs, 2014Co-Authors: Elona Agora, Jorge Antezana, Carlos CabrelliAbstract:We prove the existence of sampling sets and interpolation sets near the Critical Density, in Paley Wiener spaces of a locally compact abelian (LCA) group G . This solves a problem left by Gr\"ochenig, Kutyniok, and Seip in the article: `Landau's Density conditions for LCA groups ' (J. of Funct. Anal. 255 (2008) 1831-1850). To achieve this result, we prove the existence of universal Riesz bases of characters for L2(Omega), provided that the relatively compact subset Omega of the dual group of G satisfies a multi-tiling condition. This last result generalizes Fuglede's theorem, and extends to LCA groups setting recent constructions of Riesz bases of exponentials in bounded sets of Rd.